This invention relates to an ophthalmic lens with improved properties especially adapted for extended wear applications. More specifically, it relates to an ophthalmic lens which contains a compound capable of preventing or decreasing the release of bacterial toxins into the eye.
A dramatic shift has taken place over the past decade concerning ophthalmic lens technology, and improvements in this technology have led to changes in the manner in which ophthalmic lenses can be worn by the patient. As technology has advanced, it is now possible to wear ophthalmic lenses for extended periods of time, even during periods of sleep. This has occurred because these lenses, particularly contact lenses, have become more compatible with delicate eye tissue. Consequently, patient comfort has increased to the point where the lens can be worn by the patient for extended periods without significant discomfort. The type of contact lens which is most closely associated with extended wear applications is a soft hydrogel lens, which consists of a hydrophilic polymer swollen with a substantial amount of water.
Unfortunately, the use of ophthalmic lenses for extended wear applications has not been free of problems. For example, bacterial infections of the cornea have been reported. In the presence of minor trauma to the outer surface of the cornea (epithelium), bacteria may enter and ultimately ulcerate the cornea (ulcerative keratitis), a condition which, if not properly treated, can be responsible for sight-threatening damage to the cornea.
While attempts have been made to make contact lenses which are capable of fighting off bacterial infections in general, little has been accomplished to design a lens which is capable of preventing or decreasing the release of toxins which may cause ulcerative keratitis. The common approach has been to impregnate the lens with a broad spectrum antimicrobial. Meslard et al. (Polym. Prepr. Am. Chem. Soc., Div. Polym. Chem. 30 p. 488-489 (1989)), describe a reversible chemical immobilization of indomethacin, which is an anti-inflammatory agent, onto ophthalmic hydrogels. The drug is hydrolytically cleaved and released from the lens on the eye. Schwartz et al. (Am. J. Ophthalmol., 109, pages 701-704) describe the use of contact lenses formed from collagen to release amphotericin B, which is an anti-fungal agent, to rabbit eyes. U.S. Pat. No. 4,931,279 describes a contact lens made with an ion exchange resin and a drug such as pilocarpine, which is an anti-glaucoma agent, for release into the eye. Finally, in a broad sense, European Patent Application 219,207 describes the use of hydrophobic polymers as drug delivery agents. It is possible to make ophthalmic lenses from such hydrophobic polymers.
The prior art attempts to minimize or eliminate diseases associated with extended wear of ophthalmic lenses all have a significant drawback. Although the use of broad spectrum antimicrobials may ward off undesirable bacteria, it is also likely to kill the normal biota of the tear fluid present in the eye. The elimination of "good" bacteria may in itself cause undesirable side effects resulting from the collapse of the eye's own immunodefense system. In addition, the large scale destruction of bacteria in the eye may lead to adverse reactions because of the release of toxins associated with the lysing of bacteria.
Another approach for preventing the deleterious effects of corneal infections is disclosed in U.S. Pat. No. 4,485,029. This patent describes an aqueous solution of glyceryl monolaurate for use as a cleaning, disinfecting and preserving system, for contact lenses. While immersing this lens in this solution may preserve the lens for a longer period than what otherwise would be possible, this technique would not prevent or decrease the release of bacterial toxins when exposed to such toxins on the eye of the wearer. This is so because the amount of glyceryl monolaurate inadvertently absorbed into or on the lens is insufficient to prevent or decrease the release of bacterial toxins.
In view of the deficiencies of the prior art, it would be desirable to develop an ophthalmic lens which is capable of preventing or decreasing the production of bacterial toxins when the lens is exposed to bacteria. In addition, it would be especially desirable if such a lens could be developed which has specific activity for eliminating the ulcerative toxins associated with bacterial keratitis.